Temperature dependent behavior of thermal conductivity of sub-5 nm Ir film: Defect-electron scattering quantified by residual thermal resistivity

Abstract

By studying the temperature-dependent behavior (300 K down to 43 K) of electron thermal conductivity () in a 3.2 nm-thin Ir film, we quantify the extremely confined defect-electron scatterings and isolate the intrinsic phonon-electron scattering that is shared by the bulk Ir. At low temperatures below 50 K,  of the film has almost two orders of magnitude reduction from that of bulk Ir. The film has ∂/∂T>0 while the bulk Ir has ∂/∂T <0. We introduce a unified thermal resistivity (=T/) to interpret these completely different ~T relations. It is found that the film and the bulk Ir share a very similar ~T trend while they have a different residual part (Θ 0 ) at 0 K limit:  0~0 for the bulk Ir, and  0 =5.5 mK 2 /W for the film. The Ir film and the bulk Ir have very close ∂Θ/∂T (75 to 290 K): 6.33×10 -3 mK/W for the film and 7.62×10 -3 mK/W for the bulk Ir. This strongly confirms the similar phonon-electron scattering in them. Therefore, the residual thermal resistivity provides an unprecedented way to quantitatively evaluating defectelectron scattering ( 0 ) in heat conduction. Moreover, the interfacial thermal conductance across the grain boundaries is found larger than that of Al/Cu interface, and its value is proportional to a Corresponding author. Email: xwang3@iastate.edu, Tel: 515-294-2085, Fax: 515-294-3261 2 temperature, largely due to the electron's specific heat. A unified interfacial thermal conductance is also defined and firmly proves this relation. Additionally, the electron reflection coefficient is found to be large (88%) and almost temperature independent.3

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